Cognitive deterioration in the elderly represents an immense medical and socioeconomic burden. Nevertheless, the prognosis and course of the early stages of cognitive decline associated with senile dementia of the Alzheimer's type (SDAT) are largely unknown at the present time. This information is essential for the proper assessment of treatment modalities and for the counselling of patients and their relatives. Additionally, if we can determine the factors associated with the progression of cognitive decline, then perhaps we can alter the mechanisms so as to retard, or perhaps, ultimately, arrest the progress of the condition. We hypothesize that for a given level of cognitive impairment in SDAT, two prognostic groups will be identified. One group will have a benign course and decline very little over a 36 month period. The other group will have a malignant course and decline significantly over this period. We propose that longitudinal analyses of behavioral, electrophysiologic, neuroradiologic, metabolic, and other parameters will enable us to distinguish the benign and the malignant groups diagnostically. To test these hypotheses, we propose to follow up one hundred fifty of our patients on whom extensive baseline information has already been obtained. After a thirty-six month interval, assessment measures will be repeated in so far as is feasible, so as to establish course and prognostic concomitants.